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Tire pressure in PSI, weather forecasts in millibars or inches of mercury, scuba dive tables in atmospheres, industrial and scientific specs in pascals or bar — pressure is measured in more competing unit systems than almost any other physical quantity, because different industries adopted different standards long before anyone tried to unify them. Getting a pressure conversion wrong can matter well beyond convenience — under-inflated or over-inflated tires affect vehicle safety and fuel economy, and industrial pressure specs that are misread by a factor of ten (say, confusing bar with PSI) can lead to equipment failure. This tool exists to make that conversion fast and reliable rather than something done from memory. It converts between six common pressure units — pascals, kilopascals, bar, PSI, atmospheres, and millimeters of mercury — covering everyday automotive use, meteorology, medicine, and engineering in one place.
How it works
Pressure is fundamentally force per unit area, and every supported unit here is internally defined as a fixed multiple of the pascal (the SI base unit, equal to one newton per square meter). Enter a value, choose the unit you're converting from and the unit you want to convert to; the tool converts your input into pascals first, then converts that value into your chosen output unit. Routing every conversion through pascals means the tool only needs one conversion factor per unit rather than a separate formula for every possible pair of units.
- Enter value.
- Enter from.
- Enter to.
- Click Calculate to see your results.
Examples
Converting tire pressure
32 PSI (a common car tire pressure) converts to about 2.21 bar, or roughly 220.6 kPa.
Converting a weather reading
A barometric reading of 1013.25 hPa (millibars) — standard sea-level pressure — equals almost exactly 1 atmosphere (101,325 Pa), or about 29.92 inches of mercury in equivalent terms.
Converting a blood pressure-style reading
120 mmHg (a systolic blood pressure reading) converts to about 15,999 pascals, or roughly 16 kPa — useful for comparing across scientific unit systems.
Who should use it
- Converting tire pressure between PSI and bar.
- Converting scientific or industrial pressure readings between pascals and other units.
- Converting a weather report's barometric pressure between hPa/millibars and atmospheres.
- Cross-checking a medical pressure reading (mmHg) against a scientific unit like pascals.
Industry applications
- Automotive
- Engineering and manufacturing
- Meteorology
- Medicine and healthcare
Advantages
- Supports common everyday, automotive, medical, and scientific pressure units.
- Handles any combination of the six supported units.
- Uses a consistent, single-base-unit conversion method for reliable accuracy.
Limitations
- Doesn't include less common units like inches of mercury (inHg) or torr as separate selectable options.
- Doesn't distinguish gauge vs. absolute pressure — it converts whatever numeric value you enter.
Common mistakes to avoid
- Using bar and atmospheres interchangeably as if identical — they're close (1 atm ≈ 1.013 bar) but not exactly equal.
- Confusing PSI and kPa, which differ by roughly a factor of 6.9 — a common source of large tire-inflation errors.
- Not distinguishing between absolute pressure and gauge pressure (pressure relative to atmospheric) when interpreting a reading.
- Assuming a mmHg blood pressure reading and a mmHg barometric reading are being used in the same context, when they usually aren't interchangeable in practice despite sharing a unit.
Best practices
- For safety-critical uses like tire pressure, always double check units and use the manufacturer's specified unit directly when possible.
- When working with industrial specifications, confirm whether the source is quoting gauge or absolute pressure before converting.
- Keep at least two to three decimal places when converting between PSI and bar, since the conversion factor (about 0.0689) can introduce noticeable rounding error otherwise.
Tips
- When in doubt about tire pressure units, check your vehicle's door jamb sticker, which typically lists the manufacturer-specified PSI.
- For industrial equipment, always cross-reference the datasheet's stated pressure unit before converting to avoid a decimal-place safety error.
- If a number seems unusually large or small after conversion, double-check you haven't mixed up bar and PSI, since it's the most common mix-up.